Pathological anatomies such as tumors and lesions can be treated with an invasive procedure, such as surgery, but can be harmful and full of risks for the patient. A non-invasive method to treat a pathological anatomy (e.g., tumor, lesion, vascular malformation, nerve disorder, etc.) is external beam radiation therapy. In one type of external beam radiation therapy, an external radiation source is used to direct a sequence of x-ray beams at a tumor site from multiple angles, with the patient positioned so the tumor is at the center of rotation (isocenter) of the beam. As the angle of the radiation source changes, every beam passes through the tumor site, but passes through a different area of healthy tissue on its way to the tumor. As a result, the cumulative radiation dose at the tumor is high and the average radiation dose to healthy tissue is low.
The term “radiotherapy” refers to a procedure in which radiation is applied to a target region for therapeutic, rather than necrotic, purposes. The amount of radiation utilized in radiotherapy treatment sessions is typically about an order of magnitude smaller, as compared to the amount used in a radiosurgery session. Radiotherapy is typically characterized by a low dose per treatment (e.g., 100-200 centiGray (cGy)), short treatment times (e.g., 10 to 30 minutes per treatment) and hyperfractionation (e.g., 30 to 45 days of treatment). For convenience, the term “radiation treatment” is used herein to mean radiosurgery and/or radiotherapy unless otherwise noted.
In many medical applications, it is useful to accurately track the motion of a moving target region in the human anatomy. For example, in radiosurgery, it is useful to accurately locate and track the motion of a target region, due to respiratory and other patient motions during the treatment. Conventional methods and systems have been developed for performing tracking of a target treatment (e.g. radiosurgical treatment) on an internal target, while measuring and/or compensating for breathing and/or other motions of the patient. For example, U.S. Pat. Nos. 6,144,875 and 6,501,981, commonly owned by the assignee of the present application, describe such conventional systems. The SYNCHRONY® system, manufactured by Accuray, Inc., can carry out the methods and systems described in the above applications.
These conventional methods and systems correlate internal organ movement with respiration, using a linear model based on respiration position. However, these conventional technologies do not take into account internal organ movements along different inspiration and expiration paths. Although some internal organs may move along one path during inspiration and along another path during expiration, these conventional technologies do not distinguish these different paths because they consider only the position of the internal organ. In particular, conventional technologies use a linear approach to model the organ movement, despite the disparate inspiration and expiration paths of the internal organ. While the conventional linear modeling may have been an improvement over previous technologies, conventional linear modeling technologies are limited in their ability to model multi-path and other non-linear organ movements.